In recent years, in the field of continuous casting of a metal, various proposals have been made describing a technique for casting a thin cast plate having a thickness (2 to 10 mm) close to that of a final article by means of a continuous casting apparatus wherein use is made of a cooling drum provided with an internal cooling mechanism for the purpose of reducing the production cost and creating a new material.
In the above-described casting techniques, it is important to stably maintain the surface appearance of a cast plate on a high level. For this reason, proposals have been made on a casting technique wherein casting is conducted in the presence of an inert gas atmosphere for the purpose of preventing the formation of scum in a pouring basin (see Japanese Unexamined Patent Publication (Kokai) No. 62-130749), a roll brush technique wherein an oxide or the like deposited on the surface of a cooling drum is removed for the purpose of uniformly forming a solidified shell by means of a cooling drum (see Japanese Unexamined Patent Publication (Kokai) No. 62-176650), a technique as another means for achieving uniform formation of a solidified shell wherein a number of dimples are provided on the peripheral surface of a cooling drum so as to form an air gap serving as a heat insulating layer between the cooling drum and a solidifying shell (see Japanese Unexamined Patent Publication (Kokai) No. 60-184449), and other techniques.
Even in the above-described conventional casting techniques, it was difficult to stably prepare a cast plate having good surface appearance, and longitudinal and transversal cracks often occurred.